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Electronic Supplementary InformationExperimental section

Materials: Bismuth trichloride (BiCl3), concentrated hydrochloric acid (HCl),

ammonium chloride (NH4Cl), salicylic acid (C7H6O3), sodium citrate dehydrate

(C6H5Na3O7·2H2O), sodium nitroferricyanide dihydrate (C5FeN6Na2O·2H2O), sodium

hypochlorite solution (NaClO) and Nafion (5wt%) sodium were purchased from

Aladdin Ltd. in Shanghai. Para-(dimethylamino) benzaldehyde (C9H11NO), hydrazine

hydrate (N2H4·H2O), sodium hydroxide (NaOH), hydrochloric acid (HCl), ethanol

(CH3CH2OH), Bi foil and carbon paper were bought from Beijing Chemical

Corporation. The ultrapure water were purified through a Millipore system used

throughout all experiments.

Preparation of Bi NS/CF: Bi nanosheet array was prepared through electrodeposition

on CF. In a typical synthesis process, an aqueous solution was obtained by mixing

0.63 g BiCl3, 1.44 mL HCl and 60 mL water. Pulse current electrodeposition was

conducted in a standard three electrode system with a working electrode of Cu plate,

an Ag/AgCl reference electrode and a platinum counter electrode. Deposition of Bi

was carried out potentiostatically at –0.1 V vs. Ag/AgCl for 1 min at room

temperature (pulse deposition for 6 cycles with 10 s pulse-on and 40 s pulse-off one

cycle) and then the sample was rinsed with water for several times.

Characterization: XRD data were obtained from a LabX XRD-6100 X-ray

diffractometer with Cu Kα radiation (40 kV, 30 mA) of wavelength 0.154 nm

(SHIMADZU, Japan). SEM images were collected using the tungsten lamp-equipped

SU3500 scanning electron microscope at an accelerating voltage of 20 kV (Hitachi,

Japan). The structures of the samples were determined by TEM images on a

HITACHI H-8100 electron microscopy (Hitachi, Tokyo, Japan) operated at 200 kV.

The absorbance data of spectrophotometer were measured on SHIMADZU UV-2700

UV-Vis spectrophotometer. The N2 temperature-programmed desorption (N2-TPD)

spectrum was tested by using TP-5076 TPD experimental device. Ion chromatograph

(IC) data were acquired on Thermofisher ICS 5000 plus ion chromatography,

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2019

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contained dual temperature heater, injection valve, conductivity detector, AERS 500

Anions suppressor. 1H nuclear magnetic resonance spectra (NMR) were collected on a

superconducting-magnet NMR spectrometer (Bruker AVANCE III HD 500 MHz)

and dimethyl sulphoxide was used as an internal to calibrate the chemical shifts in the

spectra.

Electrochemical measurement: Electrochemical NRR measurements were performed

in a two-compartment cell separated by a proton exchange membrane using a CHI

660E electrochemical analyzer (CH Instruments, Inc.). The electrochemical

experiments were carried out with a three-electrode configuration using graphite plate

as the counter electrode and Ag/AgCl/saturated KCl as the reference electrode. A Bi

NS/CF electrode with area of 1 x 1 cm2 was used as working electrode. The potentials

reported in this work were converted to reversible hydrogen electrode (RHE) scale via

calibration with the following equation: E (vs. RHE) = E (vs. Ag/AgCl) + 0.197 +

0.059 × pH (V). HCl electrolyte was purged with N2 for 30 min before the

measurement.

Determination of NH3: 2 mL electrolyte was taken from the cathodic chamber, and

then 2 mL of 1 M NaOH solution containing 5% C7H6O3 and 5% C6H5Na3O7·2H2O

was added into this solution. Subsequently, 1 mL of 0.05 M NaClO and 0.2 mL of 1%

C5FeN6Na2O·2H2O were add into the above solution. After standing at room

temperature for 2 h, the UV-Vis absorption spectrum was measured at a wavelength

of 658.8 nm. The concentration-absorbance curves were calibrated using standard

NH3 solution with a series of concentrations. The fitting curve (y = 0.390x + 0.043, R2

= 0.999) shows good linear relation of absorbance value with NH3 concentration by

three times independent calibrations.

Determination of FE: The FE for N2 reduction was defined as the amount of electric

charge used for synthesizing NH3 divided the total charge passed through the

electrodes during the electrolysis. The total amount of NH3 produced was measured

using colorimetric methods. Assuming three electrons were needed to produce one

NH3 molecule, the FE could be calculated as follows: FE = (3F × cNH3 × V)/(17 × Q),

where cNH3 is the measured NH3 concentration, V is the volume of electrolyte, F is the

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Faraday constant and Q is the quantity of applied electricity. The rate of NH3

formation was firstly calculated using the following equation: vNH3 = (cNH3 × V)/(17 ×

t × A), where t is the reduction reaction time and A is the effective area of the cathode.

Determination of N2H4: A mixed solution of 5.99 g C9H11NO, 30 mL concentrated

HCl and 300 mL ethanol was used as a color reagent. Calibration curve was plotted as

follow: firstly, preparing a series of reference solutions (10 mL); secondly, adding 5

mL above prepared color reagent and stirring 20 min at room temperature; finally, the

absorbance of the resulting solution was measured at 455 nm, and the yields of N2H4

were estimated from a standard curve using 5 mL residual electrolyte and 5 mL color

reagent. Absolute calibration of this method was achieved using N2H4·H2O solutions

of known concentration as standards, and the fitting curve shows good linear relation

of absorbance with N2H4·H2O concentration (y = 0.706x + 0.033, R2 = 0.999) by three

times independent calibrations.

Details of DFT calculations: First-principles calculations were performed using the

Vienna Ab initio Simulation Package (VASP)1–3 to investigate the N2 fixation on the

rhombohedral Bi (012) surface. The valence-core electron interactions were treated by

Projector Augmented Wave (PAW)4 methods and the electron exchange correlation

interactions were described by the generalized gradient approximation (GGA) with

the Perdew-Burke-Emzerhof (PBE)5 functional. Van der Waals interactions were

considered using DFT-D3 with Becke-Jonson damping method. The surface model

was constructed with a 2×2×1 supercell containing 6 atom-layer slab, and a 15 Å

vacuum along the z direction. The energy cutoff was set to 450 eV and the convergent

criterion of geometry relaxation was set as the force on each atom is less than 0.02

eV/Å. The K points in the Brillouin zone were sampled with 3×3×1 by the

Monkhorst-Pack6 scheme. The free energy changes of the NRR steps were calculated

by the equation:7 ΔG = ΔEDFT + ΔEZPE – TΔS, where ΔEDFT is the DFT obtained

binding energy, ΔEZPE is the difference in zero-point energy correction, ΔS is entropy

change calculated by vibration analysis, and T is the temperature set to 300 K. The

free energy corrections of NH3, H2 and N2 molecules were taken from the database.

(Computational Chemistry Comparison and Benchmark Database.

4

http://cccbdb.nis.gov/.).

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Fig. S1. XPS spectrum in the O 1s region of Bi catalyst.

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Fig. S2. N2-TPD curve of Bi.

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Fig. S3. UV-Vis absorption curves of various concentrations of NH3 stained with

indophenol indicator and incubated for 2 h at room temperature. (b) Calibration curve

used to estimate the concentrations of NH3.

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Fig. S4. (a) UV-Vis curves of various concentrations of N2H4 stained with p-

C9H11NO indicator and incubated for 20 min at room temperature. (b) Calibration

curve used to calculate the concentrations of N2H4.

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Fig. S5. UV-Vis absorption spectra of the electrolytes stained with p-C9H11NO

indicator after 2-h electrolysis using Bi NS/CF at a series of potentials.

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Fig. S6. (a) IC data for different concentrations of NH4+. (b) Calibration curve

obtained from IC. (c) IC data for the electrolytes at different potentials after 4-h

electrolysis using Bi NS/CF. (d) NH3 yield rates of Bi NS/CF at different potentials

obtained from IC.

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Fig. S7. NH3 yields under different conditions using Bi NS/CF.

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Fig. S8. Control experiments results by alternately flowing N2 and Ar gas into the

electrolytes to verify the production of NH3, which were repeated three times

consecutively.

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Fig. S9. The 1H NMR spectra for 15NH4+ standard sample and the product using 15N2

as the feeding gas.

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Fig. S10. NH3 yield rates and FEs of CF, Bi foil and Bi NS/CF at –0.50 V.

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Fig. S11. (a) Long-term electrochemical stability test of Bi NS/CF at –0.50 V for 20 h.

(b) NH3 yield rates and FEs of Bi NS/CF during 24-h stability test.

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Fig. S12. NH3 yield rates and FEs of Bi NS/CF before and after 24-h stability test at –

0.50 V.

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Fig. S13. SEM image of Bi NS/CF after stability test.

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Fig. S14. XRD pattern of Bi NS/CF after stability test.

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Fig. S15. XPS spectrum in the Bi 4f region of post-NRR Bi catalyst.

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Fig. S16. Charge density difference of the *N2 and *NNH states.

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Fig. S17. Free energy profile of NRR process on (a) Bi (104) and (b) Bi (110). An

asterisk (*) denotes as the adsorption site.

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Table S1. Comparison of NH3 yield rate and FE of Bi NS/CF to produce NH3 with

other reported NRR electrocatalysts in acids under ambient conditions.

Catalyst Electrolyte NH3 yield rate FE (%) Ref.

6.89×10–11 mol s–1 cm–2

4.21 μg h–1 cm–2Bi NS/CF 0.1 M HCl

5.26 µg h–1 mg–1cat.

10.26 This work

Black phosphorus sheets 0.01 M HCl 31.37 µg h–1 mg–1cat. 5.07 8

Boron-doped graphene 0.05 M H2SO4 9.8 μg h–1 cm–2 10.8 9

N-doped porous carbon 0.05 M H2SO4 23.8 µg h–1 mg–1cat. 1.42 10

Mo nanofilm 0.01 M H2SO4 3.09×10–11 mol s–1 cm–2 0.72 11

MoO3 0.1 M HCl 29.36 µg h–1 mg–1cat. 1.9 12

MoS2/CC 0.1 M HCl 8.48×10–11 mol s–1 cm–2 0.096 13

Mo2C nanorod 0.1 M HCl 95.1 µg h–1 mg–1cat. 8.13 14

Mo2N 0.1 M HCl 78.4 µg h–1 mg–1cat. 4.5 15

MoN 0.1 M HCl 3.01×10–10 mo1 s–1 cm–2 1.15 16

Nitrogen-doped

nanoporous graphite

carbon membrane

0.1 M HCl 8 μg h–1 cm–2 5.2 17

Bi4V2O11/CeO2 0.1 M HCl 23.21 µg h–1 mg–1cat. 10.16 18

VN 0.1 M HCl 8.40 × 10–11 mol s–1 cm–2 2.25 19

Nb2O5 nanofiber 0.1 M HCl 43.6 µg h–1 mg–1cat. 9.26 20

Ti3C2Tx nanosheet 0.1 M HCl 20.4 µg h–1 mg–1cat. 9.3 21

d-TiO2/TM 0.1 M HCl 1.24×10–10 mo1 s–1 cm–2 9.17 22

B4C 0.1 M HCl 26.57 µg h–1 mg–1cat. 15.95 23

Oxygen-doped carbon nanosheet 0.1 M HCl 20.15 µg h–1 mg–1

cat. 4.97 24

Fe3S4 nanosheets 0.1 M HCl 75.4 µg h–1 mg–1cat. 6.45 25

23

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